There is known in the prior art bicycle frames which include front and/or rear shock absorbing assemblies. Examples of bicycle frames which have a rear suspension system including a shock absorber are found in U.S. Pat. Nos. 5,409,249 and 5,441,292, both of which have been assigned to the named assignee of the present application.
In the prior art, two (2) types of shock absorbers are typically incorporated into the rear suspension system of the bicycle frame. The first type of shock absorber comprises a body portion and a reciprocally movable piston rod extending axially from the body portion which facilitates viscous damping control when working in a hydraulic fluid. The piston rod defines a distal end which, in typical bicycle frame construction, is pivotally connected to the seat stay members, with the body portion being pivotally connected to a linkage member of the rear suspension system. This type of shock absorber further includes a spring member which extends between the body portion and the seat stay members, with the piston rod extending axially through the spring member.
The other type of shock absorber often incorporated into rear suspension system of the bicycle frame comprises an upper retaining plate which is rigidly attached to a linkage member of the rear suspension system, and a lower retaining plate which is rigidly attached to the seat stay members of the bicycle frame. Firmly seated between the upper and lower retaining plates is a dampening member which is typically fabricated from an elastomeric material and defines a central aperture extending longitudinally therethrough. The shock absorber further comprises a limiting cable which extends through the central aperture of the dampening member and defines opposed ends which are attached to respective ones of the upper and lower retaining plates. The dampening member is usually compressed between the upper and lower retaining plates to maintain it in position and provide a pre-load thereto, though the same is sometimes mechanically fastened to the upper and lower retaining plates.
It has been found that the elastomeric shock absorber is preferable to the hydraulic fluid shock absorber due to the enhanced dampening characteristics provided thereby and the reduced costs associated therewith. However, such elastomeric shock absorbers themselves possess certain deficiencies which detract from their overall utility. In particular, after the rear wheel of the bicycle encounters a bump or other obstruction which actuates the rear suspension system in a manner facilitating the compression of the elastomeric shock absorber, it has been found that such shock absorber has a tendency to rebound from its compressed to its uncompressed state too rapidly. This rapid rebound causes the rider to feel a jolt, thus adversely affecting the performance characteristics of the bicycle. The present invention is adapted to overcome this deficiency by providing a position sensitive friction damper which is disposed within an elastomeric shock absorber and provides dampening during the rebound thereof from the compressed to the uncompressed states, thus alleviating the undesirable performance characteristics of the rear suspension system attributable to the undamped rebound of the shock absorber.